阅读说明：本技术 掺镧层状双氧化物的制备方法、其产物及应用 (Preparation method of lanthanum-doped layered double oxide, product and application thereof ) 是由 刘超 李乃稳 帅建英 王雪颖 李寅田 安全 刘云峰 陈雯 王莹 于 2021-08-25 设计创作，主要内容包括：本发明公开了一种掺镧层状双氧化物的制备方法、其产物及应用,所述方法包括以下步骤1：制备金属硝酸盐溶液和氢氧化钠溶液；S2：将所述金属硝酸盐溶液和氢氧化钠溶液以相同的速度加入水中混合,以保持PH为恒定值,便于形成层状双氢氧化物沉淀；S3：取S1所得沉淀依次陈化、过滤、烘干、研磨、煅烧。本发明还涉及由此方法制得的掺镧层状双氧化物及其应用。(The invention discloses a preparation method of lanthanum-doped layered double oxide, a product and application thereof, wherein the method comprises the following steps of 1: preparing a metal nitrate solution and a sodium hydroxide solution; s2: adding the metal nitrate solution and the sodium hydroxide solution into water at the same speed, and mixing to keep the pH value at a constant value, so as to form a layered double hydroxide precipitate conveniently; s3: and (4) taking the precipitate obtained in the step S1, and sequentially aging, filtering, drying, grinding and calcining. The invention also relates to the lanthanum-doped layered double oxide prepared by the method and application thereof.)

1. A preparation method of a lanthanum-doped layered double oxide is characterized by comprising the following steps:

s1: preparing a solution containing metal nitrates with 2 valences and 3 valences and a sodium hydroxide solution;

s2: slowly adding the metal nitrate solution and the sodium hydroxide solution into ultrapure water at a constant speed at the temperature of 60-70 ℃ for coprecipitation, and keeping the pH constant at 10.8-11.2 in the coprecipitation process;

s3: aging and filtering the material obtained in the step S2, and then drying and grinding the material;

s4: and calcining the ground material to obtain the lanthanum-doped layered double oxide.

2. The method of claim 1, wherein: in step S1, the metal nitrates include lanthanum nitrate, ferric nitrate, and magnesium nitrate.

3. The method of claim 2, wherein: in the nitrate solution of step S1, La³⁺：Fe³⁺：Mg²⁺In a molar ratio of 1: 9: 30.

4. the production method according to any one of claims 1 to 3, characterized in that: step S2 is performed under nitrogen protection.

5. The method of claim 1, wherein: in the step S3, the aging is to keep the material obtained in the step S2 at 60-70 ℃ for at least 16-24 h.

6. The method of claim 1, wherein: the calcining temperature is 300-400 ℃, the calcining time is 2-4 h, and the temperature is increased according to 5-10 ℃/min during calcining.

7. A layered double oxide obtainable by a process according to any one of claims 1 to 6.

8. Use of the layered double oxide according to claim 7, characterized in that: the layered double oxide is used for adsorbing phosphate.

9. Use of the layered double oxide according to claim 8, characterized in that: the layered double oxide adsorbing phosphate is used as phosphate fertilizer.

Technical Field

The invention relates to the technical field of layered double oxides, in particular to a preparation method of a lanthanum-doped layered double oxide, a product and application thereof.

Background

Phosphorus is one of the major nutrient sources for aquatic organisms, but excess phosphorus leads to eutrophication of water bodies and deterioration of water quality. With the increasing frequency of human life and production activities, a large amount of phosphorus-containing industrial wastewater, agricultural wastewater and domestic sewage are generated, the phosphorus-containing wastewater still contains low-concentration phosphorus after being treated by a sewage treatment plant and is discharged into natural water bodies such as rivers and lakes, so that the content of phosphorus substances in the water body exceeds the tolerable concentration level of the water body, microorganisms, algae and other aquatic plants taking the phosphorus as nutrient substances in the water body rapidly grow and reproduce, the content of dissolved oxygen in the water body is reduced, the balance of the ecological system of the water body is damaged, and the occurrence of water body eutrophication is caused. In nature, phosphorus is usually in the form of PO₄ ^3-In the form that aquatic plants such as algae in the water body also absorb PO mainly₄ ^3-As a nutrient substance of phosphorus for reproduction and life activities, so how to remove PO from water body₄ ^3-Solving the problem of water eutrophication becomes the key point of attention of people. To date, various methods have been proposed to remove phosphate from water, including primarily biological absorption, chemical precipitation, ion exchange, and adsorption. Compared with other traditional techniques, the adsorption method has the advantages of economy, simple operation and high efficiencyCan be widely used for dephosphorization.

Layered Double Hydroxides (LDHs), also known as hydrotalcites, hydrotalcite-like or anionic clays, are anionic clays having a typical layered structure that have shown potential for many applications. The LDHs have the characteristics of inclusion for various chemical components (pollutants), variability of chemical components, easiness in crystallization and synthesis, high positive charge density of the structure and the like. The general formula for LDH is [ MII_1-xMIII_x(OH)₂]^x+[A^n- _x/n-yH₂O]^x-Wherein M (II) and M (III) are divalent and trivalent metal cations, respectively, A^n-Is an n-valent anion. Calcined derivatives of LDHs, known as Layered Double Oxides (LDO), are typically composed of mixed metal oxides or spinels. Interestingly, LDO often shows a "memory effect", that is, when mixed oxide is soaked in anion solution, the structure similar to aluminum hydroxide is reconstructed, and meanwhile, the LDO has higher anion exchange capacity, is an ideal pollutant occurrence carrier and anion exchange adsorption material, and therefore how to prepare a PO for water body₄ ^3-LDO with high-efficiency adsorption is a hot point of research nowadays to solve the problem of water eutrophication.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation method, a product and application of a lanthanum-doped layered double oxide.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a lanthanum-doped layered double oxide comprises the following steps:

s1: preparing a solution containing metal nitrates with 2 valences and 3 valences and a sodium hydroxide solution;

s2: : slowly adding the metal nitrate solution and the sodium hydroxide solution into ultrapure water at a constant speed at the temperature of 60-70 ℃ for coprecipitation, and keeping the pH constant at 10.8-11.2 in the precipitation process; the concentration and the dosage of the sodium hydroxide are based on the condition that the pH of a reaction system can be kept constant all the time;

s3: aging and filtering the material obtained in the step S2, and then drying and grinding the material;

s4: and calcining the ground material to obtain the lanthanum-doped layered double oxide.

The method of the present invention controls the pH to be constant throughout the process, in order to ensure that the cations are precipitated simultaneously, and therefore, in step S2, the prepared nitrate solution and the saturated sodium hydroxide solution are slowly added dropwise into the ultrapure water at the same time, so as to maintain the pH value required for the coprecipitation of the metal salts.

Further, in step S1, the metal nitrates include lanthanum nitrate, iron nitrate, and magnesium nitrate.

Further, in the nitrate solution of step S1, La³⁺：Fe³⁺：Mg²⁺In a molar ratio of 1: 9: 30.

further, in step S2, the whole process is performed in a nitrogen atmosphere.

The nitrogen atmosphere was conducted in order to avoid carbon dioxide in the air from entering the layered structure and substituting nitrate ions to form a carbonate interlayer. Generally, for positively charged metal hydroxide laminates, higher anions have greater binding strength than lower anions, and thus NO₃ ^-The bonding strength with the laminate is slightly stronger than that of CO₃ ^2–Corresponding LDHs may give larger intercalation levels during preparation, thus reducing the adsorption properties of the material if carbonate intercalation is formed.

Further, in step S3, the aging is to allow the material obtained in step S2 to stand at a temperature of 60 ℃ to 70 ℃ for at least 16h to 24 h.

Furthermore, the calcining temperature is 300-400 ℃, the calcining time is 2-4 h, and the temperature is increased according to 5-10 ℃/min during calcining.

Among them, the calcination temperature should not be too high, and too high temperature may change the properties of the material, resulting in collapse of the layered structure.

The invention also aims to provide the layered double oxide prepared by the method, and the specific structure is shown in the attached drawing.

The invention also aims to provide the application of the layered double oxide in adsorbing phosphate, namely the layered double oxide is used for adsorbing phosphate, and can be used as a fertilizer for crop cultivation after adsorbing the phosphate without waste discharge.

The invention has the beneficial effects that:

1. the preparation method of the lanthanum-doped layered double oxide provided by the invention has the advantages of easily available raw materials, simple and convenient operation, greenness, no pollution, easy industrialization and low cost.

2. The lanthanum-doped layered double oxide prepared by the method of the invention is a layered double oxide pair PO₄ ^3-Has excellent adsorption capacity, can be used for purifying phosphorus-containing wastewater and preventing and treating water eutrophication, and has good market prospect.

Drawings

FIG. 1 is an X-ray diffraction pattern of a lanthanum-doped layered double oxide at different calcination temperatures;

FIG. 2 is a bar graph of the phosphate adsorption capacity of lanthanum-doped layered double oxide at different calcination temperatures;

FIG. 3 is a TGA profile of the lanthanum doped layered double oxide;

FIG. 4 is an X-ray diffraction pattern of the lanthanum-doped layered double oxide at different La/(La + Fe) ratios;

FIG. 5 is a bar graph of the phosphate adsorption amounts of lanthanum-doped layered double oxides at different La/(La + Fe) ratios.

FIG. 6 is an XRD pattern (C) of MFL-1/10-350 after adsorbing phosphate

Detailed Description

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.

(I) preparation of lanthanum-doped layered double oxide

1. The preparation process comprises the following steps:

s1: preparing a solution containing 2-valent and 3-valent metal nitrates (the total metal concentration is 1mol/L, and the solution is hereinafter referred to as solution A because of the number of words in a table) and a sodium hydroxide solution (hereinafter referred to as solution B);

s2: slowly adding the metal nitrate solution and the sodium hydroxide solution into ultrapure water at a constant speed for coprecipitation at a temperature of 65 ℃ under the protection of nitrogen, and keeping the pH constant in the coprecipitation process;

s3: aging and filtering the material obtained after the S2 is subjected to coprecipitation with a water bath condition at 65 ℃, washing the material with ultrapure water, drying and grinding the material into particles with the particle size of 100 nm;

s4: and calcining the ground material to obtain the lanthanum-doped layered double oxide.

2. The process conditions of each example are shown in the following table, wherein the concentration of the sodium hydroxide solution is controlled at 2mol/L, and the amount is based on the maintenance of the pH of the reaction system.

(II) preparing lanthanum-doped layered double oxides at different calcination temperatures and times, and performing performance test of adsorbing phosphate, wherein the preparation method is as described in the first part, and the process conditions for preparing the lanthanum-doped layered double oxides are as in examples 2-5:

that is, the mixture was calcined at 250 ℃, 350 ℃, 450 ℃ and 550 ℃ for 3 hours, and the remaining 1 group was not calcined, and the XRD patterns of the 5 parts of the product obtained were as shown in FIG. 1.

And (3) adding the 5 parts of the product into phosphate solution with equal concentration respectively, then oscillating and adsorbing for 24 hours in a constant-temperature oscillation box, detecting the concentration of the residual phosphate in the solution and calculating the adsorption quantity, wherein the result is shown in figure 2.

(III) taking the sample of the example 1, measuring the TGA curve at 0-1000 ℃ in a thermogravimetric analyzer, wherein the result of the TGA curve is shown in figure 3.

(IV) lanthanum-doped layered double oxides were prepared at different La, Fe and Mg ratios and tested for phosphate adsorption performance, as described in section (I), using the same process conditions as in examples 6-9:

the XRD patterns of the 5 parts of product obtained in comparative example 1 and examples 6-9 are shown in FIG. 4.

And fifthly, taking 5 parts of the product obtained in the fourth part, respectively adding the product into phosphate solution with equal concentration, then oscillating and adsorbing the product in a constant-temperature oscillation box for 24 hours, detecting the concentration of the residual phosphate in the solution and calculating the adsorption quantity, wherein the result is shown in figure 5.

(VI) testing the reconstruction characteristics of the material of the invention, taking the sample of example 1 as the object

As shown in FIG. 6, the characteristic diffraction peaks of the material (denoted as MFL-1/10-350) before and after adsorption of phosphate did not change significantly. However, after 20mg/L of phosphate is adsorbed, the material has a layered double hydroxide structure, which indicates the characteristic 'memory effect' of the material and causes the structural reconstruction. At lower phosphate concentrations, the main adsorption mechanism is the process of reconstitution, while at higher phosphate concentrations, surface precipitation.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.